This section provides information helpful in understanding the invention but that is not necessarily prior art.
The use of lithium-ion batteries to power electric motors in automotive vehicles and in other high-energy devices and equipment has led to the need for higher gravimetric capacity and higher volumetric capacity batteries. While graphitic carbon is a durable and useful lithium-intercalating material for a negative electrode (anode) in lithium-ion cells, it has a relatively low capacity for such lithium insertion. Other potential electrode materials such as silicon (theoretical capacity, 3579 mAh/g for L15Si4) and tin (theoretical capacity, 992 mAh/g for Li22Sn5) have much higher theoretical capacities than graphite for lithium insertion. However, the volume changes of up to 300 volume percent for silicon during lithiation and delithiation processes leads to the fracture of the active silicon material and a resulting loss of electrical contact with the conductive additives or with the current collectors to which the anode particles are attached. Tin has a like problem of large volume expansion upon lithiation, which again leads to rapid capacity degradation.
Electrodes containing silicon-based materials have been prepared by forming a slurry of silicon particles or silicon oxide (SiOx) particles, graphite, and conductive carbon particles with a polymeric binder solution or dispersion. For example, Yu, International Application (PCT) Publication No. WO 2016/082120, which is hereby incorporated herein by reference in its entirety, describes forming a porous layer of electrode particles on a surface using an atmospheric plasma spray device. A non-plasma spray device is then used to spray an aqueous solution of polymeric binder material onto the porous layer. The water evaporates and the polymeric binder bonds the particles together and to the surface.
Gayden, US Patent Application Publication 2016/0254533, which is hereby incorporated herein by reference in its entirety, describes the use of an atmospheric plasma stream in making electrodes for lithium-ion cells and batteries. In the described method, particles of lithium-ion accepting and releasing electrode material are coated with or mixed with particles of conductive metals. The electrode material particles pre-coated with metal or mixed particles of metal and electrode material (for example either copper-coated silicon particles or a mixture of copper particles and silicon particles) are delivered into a plasma stream that partially melts the metal before being deposited on a substrate to form an electrode. The electrode material particles may be in the range of tens of nanometers to tens of microns. The US 2016/0254533 method is said to avoid the need for organic binders and allow deposition of thicker, lower stress layers of active electrode materials for higher cell capacity and power.
Deng et al., US Patent Application Publication 2017/0121807, which is hereby incorporated herein by reference in its entirety, describes methods of forming electrode material in which non-metallic particles of electrode material for a lithium secondary cell are coated with particles of an elemental metal before being placed in an atmospheric plasma stream and deposited in a continuous layer on a substrate. The metal particles are melted sufficiently during the deposition to bond the non-metallic electrode material particles to each other and to the substrate.
Deng et al., US Patent Application Publication 2017/0301958, which is hereby incorporated herein by reference in its entirety, describes atmospheric plasma spray depositing devices to sequentially form multiple layers of a lithium-ion cell for a lithium battery. Thus, a suitable substrate layer is conveyed past a series of plasma spray devices to form, in sequence, a current collector layer, a particulate electrode material layer, a porous separator layer, an opposing electrode layer, and a second current collector layer.
Yu et al., US Patent Application Publication 2017/0309888, which is hereby incorporated herein by reference in its entirety, describes coating active electrode material with a liquid precursor dispersion that, when exposed to an atmospheric plasma at a predetermined energy level and temperature up to 3500° C., is converted to carbon or metal oxide, and the carbon or metal oxide coated active electrode material is deposited onto a substrate in forming an electrode.
There remains a need for a method of forming lithium ion cell electrodes from materials with high theoretical capacities, such as silicon-containing and metal-containing negative electrode material structural compositions, that are more durable and maintain higher capacity during use in lithium-ion batteries.